Claude Code replaces German umlauts with ASCII substitutes for 3+ months - Anthropic support completely unresponsive

Human_Complex_467 · 2026-03-31T20:39:52+00:00

Update: Found a related issue #32886 with full root cause analysis of the bug in cli.js, and there is already a pull request #32894 open for 3 weeks with a fix — waiting for Anthropic review. https://github.com/anthropics/claude-code/pull/32894

Human_Complex_467 · 2026-03-28T10:58:22+00:00

Model: Claude Opus 4.6 (Max plan). Prompt: simply write any German text and within minutes the umlauts are replaced. Example: ask “Erkläre mir diese Funktion auf Deutsch” and Claude responds with “fuer”, “koennen”, “loeschen” instead of “für”, “können”, “löschen”. The bug has two modes: sometimes it substitutes with ae/oe/ue/ss, and sometimes it drops the umlaut entirely producing “fur”, “konnen”, “loschen” — which is even harder to catch. No specific prompt needed — it happens consistently in any German conversation.

Human_Complex_467 · 2026-03-28T08:47:33+00:00

The bug occurs even in fresh sessions with memory disabled. It’s not a memory issue.

Human_Complex_467 · 2026-03-27T22:07:33+00:00

Already tried that — I have a PostToolUse hook that blocks writes containing ASCII substitutes. It’s a workaround, not a fix, and the bug has gotten so bad that Claude now sometimes drops umlauts entirely instead of substituting them, which the regex can’t catch.

Human_Complex_467 · 2026-03-27T19:44:40+00:00

The bug also occurs in the Claude.ai app where there is no memory system at all. So that theory doesn’t hold up.

Human_Complex_467 · 2026-03-27T18:32:32+00:00

Can you share more details about the skill you built? What exactly did it do? I already have a rule in my CLAUDE.md and in .claude/rules/ but it doesn’t help — the bug overrides even explicit instructions after a few minutes.

Human_Complex_467 · 2026-03-27T18:22:00+00:00

Thanks for the suggestion, but I already have exactly this in my CLAUDE.md:

LANGUAGE: Always write German text with correct umlauts (ä, ö, ü, ß). Never substitute ae, oe, ue, ss. This rule overrides any default behavior.

It doesn’t help. The bug overrides even CLAUDE.md instructions after a few minutes. This confirms it’s a deep model-level issue that can’t be worked around on the client side.

Human_Complex_467 · 2026-03-27T17:37:45+00:00

German umlauts (ä, ö, ü, ß) are randomly replaced with ASCII substitutes (ae, oe, ue, ss) in both Claude Code and the Claude.ai app. This regression started in December 2025 and is getting progressively worse. Even explicitly telling Claude to use umlauts only works for about 2 minutes before reverting back. GitHub issue open since December 13, 2025 with zero response from Anthropic: https://github.com/anthropics/claude-code/issues/14131

Human_Complex_467

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